It could be system files though it's strange to have so many. make sure your computer is virus free with an antivirus program.
You can also try two things with CCleaner (free) Link Removed
Download and install it.
First, go to Options\Settings and check ""Add "Run CCleaner" option to Recycle context menu. Then close CCleaner.
Right click your recycle bin and click "Run CCleaner". It will run for a few seconds. Then check if the files are gone.
If that didn't work, try this:
Tools\Drive Wiper\ Make sure the first option is set to "Free Space Only", and the second option is Simple Overpass (1 pass). Then click the button "Wipe" and let it do it's thing. Then check again if the files are gone and report back.